1. Field of the Invention
The present invention relates to a method of growing a III group nitride single crystal, and more particularly, to a method of manufacturing an a-plane gallium nitride (GaN) single crystal by using an metal-organic chemical vapor deposition (MOCVD) process.
2. Description of the Related Art
In general, a gallium nitride (GaN) single crystal is grown on a hetero-substrate such as a sapphire Al2O3 and a silicon carbide SiC by using one of gas-phase growth method such as metal-organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE) and molecular beam epitaxy (MBE). In an actual method of manufacturing a GaN light emitting device, a GaN single crystal grown in a c-axis direction [0001] of the hetero-substrate is used.
However, since strong piezoelectric properties are shown in the c-axis direction [0001], a piezoelectric field occurs due to a stress on an interface between thin films with different constants. As shown in FIG. 1A, in a band diagram of an ideal active layer without stress, wave functions of electrons and electron holes are approximately symmetrical to each other.
On the other hand, as shown in FIG. 1B, when a compressive stress is applied due to a difference of lattice constant, a distance between wave functions of electrons and electron holes becomes more distant due to the piezoelectric field, as shown as a dotted line.
Accordingly, the active layer of the GaN-based device grown in the c-axis direction of the substrate has a chronic problem of a decrease in recombination efficiency. On the other hand, since the distance between the wave functions due to an effect caused by the piezoelectric field, a light emitting wavelength shows a tendency to be lengthened and a wavelength of the light emitting device may be varied depending on the degree of voltage application.
To solve the problems, U.S. Patent Publication No. 2003/0198837 (published on Oct. 23, 2003, Michael D. Craven et al.) discloses a method of growing nonpolar a-plane GaN. According to the described document, it is disclosed that the nonpolar a-plane GaN is grown only at a low pressure of 0.2 atm or less. The low-pressure growth condition has a limitation on obtaining high quality crystallinity, which is well-known to those skilled in the art. Actually, it may be known that the a-plane GaN disclosed in the document has a plurality of pits in the shape of a stripe pattern.
As described above, in conventional methods of growing an a-plane GaN, there is a limitation on obtaining a mirror-like surface having high quality surface morphology.
To solve the problem, a combination with additional crystal-improvement process such as lateral epitaxial overgrowth (LEO) has been tried. However, in the growth method, not only an additional process is required but also a use area and a size of a device are limited.